XVoice provides voice control of X applications using IBM's ViaVoice for Linux (free download at their web site). Both user-defined commands and dictation are supported. It can be used to write letters, write code, control netscape, etc.

Kymaera is a open-source Front End for many applications. It was originally designed as a FrontEnd for MAME and other EMU's for use on Arcade Cabinets. The current version of Kymaera 2.0.2 is for Windows and DOS. Linux version coming soon

The Open Mind Speech project is part of the Open Mind Initiative and aims to develop free(GPL) speech recognition and signal processing (DSP) tools and applications, as well as collect speech data from "e-citizens" using the Internet.

SnackAmp is a powerful multi-platform audio music (mp3, ogg ,wav, streams ...) player and organizer for large music collections. Manage your entire collection, including ID3 tagging and auto-playlisting. Integrated web server for remote control/strea

libdlna aims at being the reference open-source implementation of DLNA (Digital Living Network Alliance) standards. Its primary goal is to provide DLNA support to build both DLNA servers and players in the long term.

Tom's Audio Processing plugins is a selection of LADSPA plugins for audio engineering on the Linux platform. Intended for use in a professional DAW environment such as Ardour, it includes high quality reverberation, echo, eq, limiter & more.

General Sound Interface (GSI).
This is a sound interface capable of controlling every detail of sound playing. It can use the following interfaces: OSS, Ultrasound (Linux 2.0.x & 2.1.x), FreeBSD (pcm), and generic /dev/audio.